The present invention relates to a sensor for detecting any approach or contact of a human body.
In a conventional human body detection sensor, an electric signal generated by an oscillation circuit is inputted to a detection circuit including a detection capacitor, which is provided so as to change its capacitance due to the approach of a human body, as well as to a reference circuit equivalent to the detection circuit conditioned by no approach of any human body to the detection capacitor, and through a comparison between an output of the detection circuit and an output of the reference circuit, any change in waveform or phase of the output of the detection circuit is detected, by which approach of a human body to the detection capacitor is detected. However, with such a human body detection sensor, in particular, the more the capacitances of the detection capacitor and the connecting line for connecting the detection capacitor are large, the more the capacitances of the detection capacitor and the connecting line change due to temperature. As a result of this, there has been an issue that constant detection results could not be obtained because of changes in the output of the detection circuit due to temperature.
Japanese Patent Laid-Open Publication No. H07-189538 discloses a human body detection sensor provided with a temperature compensation circuit that, through a comparison between outputs of a detection circuit and a reference circuit, changes the threshold value, which serves as a reference for decision as to approach of a human body to the detection capacitor, depending on temperature detected by a thermistor. In this case, however, there is an issue that providing a multiplicity of detection capacitors would make it necessary to provide the same number of reference circuits and temperature compensation circuits as well. Further, Japanese Patent Laid-Open Publication No. 2002-295094 discloses a sensor which has two detection capacitors and, through a comparison outputs of their respective antenna circuits, decides as to whether or not any human body is approaching. However, there is a problem that this sensor is applicable only to cases where any human body approaches only one of the two detection capacitors.